The present invention generally relates to a seatbelt retractor which takes up a seatbelt so as to be windable and extractable and more specifically relates to a seatbelt retractor having a seatbelt load restricting mechanism.
Conventionally, seatbelt devices are provided in vehicles, such as automobiles, in order to restrain the passengers in the event of emergencies. The seatbelt devices help restrain passengers in their seats, thereby protecting the passengers.
Modern seatbelt devices typically have seatbelt retractors for taking up the seatbelt. The seatbelt retractor is arranged such that, in the event the seatbelt is not being worn, the seatbelt is taken up on a spool. In the event that the seatbelt is worn, the seatbelt is extracted and worn by the passenger and excess webbing is taken up on the spool. Further, the seatbelt retractor is arranged such that a lock mechanism operates in the event of an emergency. The lock mechanism hinders the rotation of the spool in the direction of extracting the seatbelt, thereby impeding the extraction of the seatbelt. Thus, the seatbelt restrains and protects the passenger in the event of an emergency.
With conventional seatbelt retractors and seatbelt devices, a rapid vehicular deceleration occurring while the seat belt is worn results in great inertia that moves the passengers forwards. Thus, an increased load is placed on the seatbelt and the passenger is subjected to an increased shock force from the seatbelt. This shock force on the passenger is not necessarily a problem. However, it is desired to reduce this force. Accordingly, conventional seatbelt retractors have been developed with a torsion bar, so as to restrict the load placed upon the seatbelt in the event of an emergency while the seatbelt is worn.
FIG. 11 is a cross-sectional diagram illustrating an example of a seatbelt retractor having such a torsion bar. In the Figure, reference numeral 1 denotes a seatbelt retractor, 2 denotes a frame in the shape of a box with one end open and 3 denotes a seatbelt. Numeral 4 denotes a spool which is rotatably supported by both side walls of the frame 2. The spool 4 takes up the seatbelt 3. Numeral 5 denotes a deceleration detecting means. The detecting means 5 detects vehicular deceleration generated in the event of an emergency and operates accordingly. Numeral 6 denotes a lock mechanism. The deceleration detecting means 5 activates the lock mechanism 6. The lock mechanism 6 hinders the rotation of the spool 4 in the direction of extracting the belt. Numeral 7 denotes a torsion bar which is movably mounted. The torsion bar 7 passes through the center of the spool 4 in the axial direction and rotationally links the spool 4 and the lock mechanism 6. Numeral 8 denotes a first spring for perpetually pressing the spool 4 in the direction of taking up the belt. A second spring 9 works in conjunction with the first spring 8 via a bushing 10. Numeral 11 denotes a pretensioner which generates belt take-up torque in the event of an emergency. Numeral 12 is a bushing for transmitting the seatbelt take-up torque from the pretensioner 11 to the spool 4.
The lock mechanism 6 is provided with a locking base 14 which is capable of integrally rotating with a later-described first torque transmitting shaft 17 of the torsion bar 7. The lock mechanism 6 also holds a pawl 13 in a manner capable of rocking. The torsion bar 7 is provided with a lock gear 6a which normally rotates integrally with the torsion bar 7 but stops in the event of an emergency by the operation of the deceleration detecting means 5. The lock gear 6a generates a relative rotational difference with the torsion bar 7 and engages the pawl 13 with inner teeth 19 on the side wall of the frame 2. The engagement of the pawl 13 with the inner teeth 19 hinders rotation of the locking base 14. Thus, the spool 4 stops in the direction of extracting the seatbelt.
A first torque transmitting portion 17, which engages the locking base 14 in a manner incapable of relative rotation, is formed on the torsion bar 7. A second torque transmitting portion 18 is formed on the torsion bar 7. The second torque transmitting portion 18 engages the spool 4 in a manner incapable of relative rotation.
The spool 4 is perpetually pressed by the spring force of the spring 8 in the direction of taking up the seatbelt. The spring 8 acts via the bushing 10, torsion bar 7, second torque transmitting portion 18 of the torsion bar 7, and the bushing 12. Also, in the event of the pretensioner 11 operating, the belt take-up torque generated at the pretensioner 11 is transmitted to the spool 4 via the bushing 12. Thus the spool 4 takes up a predetermined amount of the seatbelt 3.
With conventional seatbelt retractors 1 thus configured, the seatbelt 3 is completely taken up by the pressing force of the spring means 8 when the seatbelt is not being worn. Extracting the seatbelt 3 at a normal speed for wearing causes the spool 4 to rotate in the seatbelt extracting direction, which allows the seatbelt 3 to be extracted smoothly. An tongue (not shown) provided to the seatbelt 3 is inserted into and retained by a buckle fixed to the vehicle body. The portion of the seatbelt 3 which has been excessively extracted is taken up by the spool 4 by the pressing force of the spring means 8. Thus, the seatbelt 3 is adjusted so that the passenger does not feel too tight.
In the event of an emergency, the seatbelt take-up torque generated by the pretensioner 11 is transmitted to the spool 4. The spool 4 takes up the seatbelt 3 by a predetermined amount, thereby securely restraining the passenger. Under rapid vehicular deceleration generated in the event of an emergency, the deceleration detecting means 5 activates the lock mechanism 6. That is, the rotation of the lock gear 6a in the direction of extracting the seatbelt is obstructed by the operation of the deceleration detecting means 5. The pawl 13 of the lock mechanism 6 rotates and engages the inner teeth 19 of the side wall of the frame 2. This impedes the rotation of the locking base 14 in the direction of extracting the seatbelt. The spool 4 alone rotates in the direction of extracting the seatbelt relative to the locking base 14. Subsequently, the spool 4 rotates in the direction of extracting the seatbelt while twisting the torsion bar 7. Therefore, the load placed on the seatbelt 3 is restricted by the twisting torque of the torsion bar 7. Thus, the shock to which the passenger is subjected is absorbed and alleviated.
An energy absorbing (EA) mechanism is formed by the torsion bar 7. The properties of load restriction under this EA mechanism at this time (hereafter also referred to as EA load) are such that the load restricted by the torsion bar 7 gradually increases as the stroke of relative rotation of the spool 4 to the locking base 14 increases. This is shown by the dotted line in FIG. 2(a). The load later becomes a constant value F1.
Additionally, the conventional seatbelt retractor 1 is arranged so that the locking base 14 of the lock mechanism 6 rotates in the direction of extracting the seatbelt relative to the lock gear 6a if seatbelt is rapidly extracted. Accordingly, the pawl 13 of the lock mechanism 6 engages the inner teeth 19 of the side wall of the frame 2 in the same manner as above. Thereby, the rotation of the locking base 14 is obstructed. Therefore, the rotation of the spool 4 in the direction of extracting is obstructed via the torsion bar 7, and extraction of the seatbelt is obstructed.
With such a conventional seatbelt retractor 1, a single EA load is set by the torsion bar 7 alone, and the kinetic energy of the passenger is absorbed by only this one EA load. A minimum and constant EA load F1 is selected for this EA load. It is chosen such that the kinetic energy of the passenger can be absorbed, so as to be able to reduce the shock load on the passenger as much as possible.
Even though the kinetic energy of the passenger in an emergency can be absorbed with a conventional EA mechanism made up of only a torsion bar 7, it is desirable that the kinetic energy of the passenger be absorbed in an optimally efficient and more appropriate manner.
The present invention has been made in light of the need for an EA mechanism which absorbs kinetic energy in a more efficient. It is an object thereof to provide a seatbelt retractor wherein the restriction load placed on the seatbelt can be flexibly set so that the kinetic energy of the passenger is absorbed in a more efficient manner.
The present invention provides a seatbelt retractor comprising at least: a spool for taking up a seatbelt, a lock mechanism having a locking member whereby rotation in the direction of extracting the seatbelt is obstructed in the event of an emergency, a torsion bar rotatably linking the spool and the locking member, and capable of being deformed by twisting, and a seatbelt load restricting mechanism for restricting the load placed upon the seatbelt wherein the torsion bar deforms by twisting at the time that the rotation of the locking member in the direction of the seatbelt being extracted is obstructed and the spool rotates relative to the extracting direction of the seatbelt, wherein the restriction load properties of said seatbelt load restricting mechanism comprise a relatively small restriction load due to twisting deformation of the torsion bar alone, and a relatively great restriction load made up of a restriction load due to twisting deformation of the torsion bar and a restriction load due to another member, and wherein the relatively great restriction load is set to have properties which change in a plurality of steps.
The present invention also provides a seatbelt retractor, wherein the seatbelt load restricting mechanism further comprises a predetermined number of share pins provided between the spool and the locking member such that a shearing load is placed thereupon at the time of the relative rotation of the spool, wherein the restriction load initially greatly increases the shearing load on the share pins and is set to a constant load by the twisting load of the torsion bar following the shearing destruction of the share pins.
The present invention also provides a seatbelt retractor wherein an indented portion is formed in the share pins, and the relative rotation position of the spool is set such that the share pins break under shearing at this indented portion.
Additionally, the present invention provides a seatbelt retractor, wherein a plurality of the share pins are provided, and the relative rotational position of the spool where the share pins break under shearing is set so as to be different for each share pin.
The present invention also provides a seatbelt retractor, wherein the seatbelt load restricting mechanism further comprises a cut portion provided to one of the spool and the locking member, and a cutting blade which is provided to the other of the spool and the locking member and which cuts this cut portion at the time of relative rotation of the spool, wherein said restriction load initially rises greatly due to the cutting resistance at the time of the cutting blade cutting the cut portion but is set at a constant load due to twisting deformation of the torsion bar following completion of cutting of the cut portion.
The present invention provides a seatbelt retractor, wherein a plurality of the cut portions are provided, and wherein a plurality of cutting blades are provided corresponding to these cut portions, and the relative rotation position of the spool where these cut portions are cut by the corresponding cutting blades is set so as to be different for each cut portion.
With the seatbelt retractor according to the present invention thus configured, the restriction load for restriction placed on the seatbelt in the event of an emergency comprises a relatively smaller restriction load and a relatively greater restriction load. The smaller restriction load is due to twisting deformation of the torsion bar while the large restriction load is made up of a restriction load due to twisting deformation of the torsion bar and a restriction load due to twisting deformation of another member. The great restriction load is controlled such that it changes in multiple steps. This is due to the restriction load properties of the seatbelt load restricting mechanism. Thus, effective use of these restriction load properties allows the restriction load to be flexibly adjusted. Accordingly, the kinetic energy of the passenger can be absorbed in an optimally efficient and more appropriate manner.